Powershift transmissions control gear ratio changes in accordance with a predetermined shift map which is a function of transmission output speed. In particular, each gear ratio has an associated upshift and downshift point that is preset at the factory. However, each upshift point is a compromise between an aggressive shift point that provides optimum work machine performance and a conservative shift point which prevents hunting, i.e. repetitive upshifting and downshifting. Hunting can cause poor engine performance as well as increase the wear and tear on various transmission components. As a result, if a single upshift point is used, it must be conservative to prevent the undesirable results of hunting.
Conservative shift points occur at higher speeds where it is less likely that the transmission will downshift and begin hunting. When shifting at higher speeds, the power output through the transmission can drop significantly prior to the upshift. This drop in power prior to the upshift is undesirable, especially when rapid acceleration is requested by the operator of the work machine. In fact, during rapid acceleration, a more aggressive shift point can be used with a lessor risk of hunting. Thus, upshifting at the conservative shift point has the drawback of limiting the performance of the work machine when rapid acceleration is requested by the operator.
What is needed therefore is a method and apparatus for adaptively selecting either the aggressive shift point or the conservative shift point which overcomes the above-mentioned drawbacks.